The claimed invention relates generally to the field of disc drive data storage devices and more particularly, but not by way of limitation, to an improved disc clamp assembly used to secure a number of discs to a spindle motor hub assembly in a disc drive disc stack assembly.
A disc drive is a data storage devices used to store digital data. A typical disc drive includes a number of rotatable magnetic recording discs which are axially aligned and mounted to a spindle motor for rotation at a constant, high speed. A corresponding array of read/write heads access tracks defined on the respective disc surfaces to write data to and to read data from the discs.
A disc clamp assembly is used to clamp the discs (and intervening disc spacers) to a spindle motor hub. The disc clamp assembly applies an axially directed clamping force to the resulting disc stack to secure the discs and spacers to the hub. A greater clamping force generally improves the ability of the disc stack to resist disc shifting in response to the application of mechanical shocks to the disc drive. However, the application of too great a clamping force upon the disc stack can induce undesired mechanical distortion of the discs. Localized variations in the amount of clamping force upon the topmost disc can also induce distortion of the discs.
With the continued industry trend of providing disc drives with smaller overall sizes and greater amounts of data storage capacity, the size of various disc drive components has been reduced, including reductions in the thickness of each disc. As the discs become thinner, the maximum amount of clamping force that can be applied to secure the discs to a spindle motor hub without causing mechanical distortion of the discs is also generally reduced.
Prior art disc clamp assemblies typically engage a feature of the spindle motor to exert the clamping force upon the discs. Such engagement can be accomplished through the use of threaded screws which fasten a clamp member to the spindle motor hub. The desired clamping force is exerted in relation to the torque applied to the screws. Other engagement methodologies have involved the use of interference fits between the clamp member and the spindle hub to wedge or otherwise lock the clamp member in place. These and other prior art disc clamp assemblies can readily generate undesired particulate contamination within the disc drive.
Moreover, during installation of such disc clamp assemblies a large axial force is applied to the spindle motor hub, which can undesirably result in the application of large axially directed forces to ball bearing assemblies used to rotate the spindle motor hub relative to a central shaft. Such forces can deform or otherwise damage the bearing assemblies, inducing runout errors during subsequent rotation of the discs. Such errors become increasingly undesirable with continued increases in track densities in subsequent generations of drives.
Further, prior art disc clamp assemblies can require significant assembly resources to install and correctly set the desired clamping force. Screw-type clamps require insertion and torquing of multiple threaded fasteners; interference-fit type clamps typically require complicated tooling to manipulate the various elements to achieve the final clamping configuration. Subsequent removal of the clamping assembly can also require significant resources and can lead to further generation of particulate contamination.
U.S. Pat. No. 5,101,306 issued to Johnson illustrates such deficiencies with the prior art. Johnson ""306 discloses a rigid grip ring which engages a spindle motor hub. A push-on retaining ring is pressed down over in sliding contact with the grip ring to a final engagement position within a detent of the grip ring, after which the retaining ring bears against the grip ring to apply a clamp force to a disc stack. Johnson ""306 potentially generates significant particulate contamination, requires relatively complicated tooling to install and subsequently remove the retaining ring, and applies significant axially-directed forces upon the spindle motor bearing assemblies during both installation and deinstallation of the retaining ring. Johnson ""306 further appears to require manual (hand) operations to install and deinstall the clamp and is thus not readily adaptable for use in high volume automated assembly environments.
There is a need, therefore, for an improved disc clamp assembly which overcomes these and other deficiencies in the prior art and which applies more consistent and controlled axially directed clamping forces upon the discs and the spindle motor of a disc drive.
In accordance with preferred embodiments, a disc stack assembly is provided for a disc drive. The disc stack assembly includes a disc clamp assembly which clamps a number of discs to a rotatable hub of a spindle motor.
The disc clamp assembly includes a substantially disc shaped clamp plate and an annular retaining ring. The clamp plate has an inner ring engagement portion, an outer disc engagement portion, and an initial, substantially planar shape in an undeformed state. The retaining ring preferably has a generally split-ring configuration and is secured in an annular ring recess of the spindle motor hub.
The retaining ring maintains the clamp plate in a conically deformed state so that the inner ring engagement portion of the clamp plate applies a first moment force against the retaining ring while the outer disc engagement portion of the clamp plate applies a second moment force as an axially directed clamping force upon the disc. In this way, controlled clamping force can be applied to clamp the disc to the spindle motor without imparting significant axially directed force to a bearing assembly of the spindle motor.
These and various other features and advantages which characterize the claimed invention will be apparent from a reading of the following detailed description and a review of the associated drawings.